Single rack backspace



Jan. 30, 1968 R. E. HOSEY ETAL 3,366,215

SINGLE RACK BACKSPACE Filed July 28, 1965 United States Patent 3,366,215 SINGLE RACK BACKSPACE Richard E. Hosey, Jerome B. GDaniel, and Richard J. Young, Lexington, Ky., and Donald A. Decker, Dallas, Tex., assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed July 28, 1965, Ser. No. 475,431) 7 Claims. (Q1. 197-91) ABSTRACT 01* THE DISCLOSURE Step-by-step forward and reverse spacing is accomplished in a typewriter through the use of a single pawl and single rack, by reliance upon the inertia of a large mass portion of the typewriter to perform a holding function heretofore accomplished through the use of a separate rack or pawl.

Description of the invention In printing devices such as typewriters, teletypew-riters, computer printout mechanisms, etc., lines are printed a character at a time using mechanism that moves a printing station along the paper. Normally, the printing station is moved in a forward direction for printing under the control of a gear and pawl combination. However, functions such as error correction, underlining, etc, require step-'by-step rearward movement, or backspacing. This invention employs the differential mass of a small control member and a large printing component, i.e., a print head carrier or platen mechanism, and the inertia characteristics of such difierential mass to achieve the backspace function as well as normal escapement with a single gear and pawl combination.

Movement of a printing station is ordinarily accomplished by a continuously applied source of energy and an es-capement mechanism for selectively permitting movement under the influence of the source of energy. Conventional escapement mechanisms include a pair of pawls that operate on the principle of a verge, such that one pawl holds the escapement gear while the other pawl moves to a new position thereon, and vice versa. In -U.S. Patent 3,126,998, entitled Escapement Mechanism for Typewriter, issued to Leon E. Palmer, Mar. 31, 1964, there is described an escapement system wherein normal escapement control is accomplished by a single pawl that is withdrawn from an escapement gear for a predetermined period of time and then reinserted to permit an escapement movement determined by the period of time. The backspace or rearward stepping movement associated in practice with the mechanism of the prior patent, employs a separate backspace rack and pawl for driving the printing station rearwardly where it is held by the main escapement rack and pawl while the backspace mechanism is restored.

This invention eliminates the need for separate forward and rearward escapemen-t racks and relies on the differential mass, as stated above, to retain the printing station fixed during restoration from a backspacing operation. This concept is implemented by the provision of a powered actuating mechanism for operational control of the back-space mechanism whereby the printing station is first moved rearwardly by machine power storing energy in appropriately located springs. After specified movement, the power is abruptly released or unloaded permiting reverse acceleration of the parts by the springs. The lower mass control part will accelerate much faster than the higher mass printing component, thus permitting restoration of the control part without positive mechanical retention of the printing component.

Patented Jan. 30, 1968 Another phase or novel concept of this invention involves the provision of mechanism permitting limited manual adjustment of the printing station location for op erator orientated flexibility in making corrections that require, for example, crowded or expanded letter spacing. This mechanism provides for simply shifting the datum of the escapement control member within a limited range to provide positive variable positioning of the printing station.

Accordingly, it has been an object of this invention to provide a simplified escapement control mechanism for performing both normal and backspace printing station movement.

Another object of this invention has been to provide an escapement control mechanism that is compact as well as simple in construction, to provide savings of space as well as cost.

A further object of this invention has been to provide mechanism for manually adjusting the printing station location for correction of errors requiring an extraordinary spacing, such as crowding or expanding the length of words.

These and other novel concepts and objects of this invention will be apparent to those skilled in the art upon reading the following description of a preferred embodiment thereof wherein specific reference is made to the accompanying drawing, of which:

FIGURE 1 is a rear perspective view of printing mechanism employing this invention, partially broken away and somewhat simplified for ease of understanding; and

FIGURES 2, A, B, and C are partial schematic operational plan views of mechanism similar to that shown in FIGURE 1 illustrating the major operational steps of a backspace operation.

Referring now more particularly to the drawings, in FIGURE 1 'a printing device 10, such as a typewriter or printer component of a communicating or computing machine, is shown comprising a stationary frame or supporting part 11, on which is mounted a conventional platen or other printing media support means 12. The platen 12 is mounted for rotation on the frame, but is held laterally fixed relative thereto. The platen 12 cooperates with print forming means such as a typehead 13, as described in US. Patent 2,919,002, entitled Selection Mechanism for a Single Printing Element Typewriter, issued to Leon E. Palmer, Dec. 29, 1959, to cause printing at a printing station or zone S. In FIGURE 1 the typehead 13 is shown supported on a carriage or carrier 14 that is movable laterally upon a stationary guide bar or track 15. It is to be understood, however, that this invention is equally applicable to mechanism having a stationary typehead and a carriage mounted platen as in the case of most typebar typewriters.

The carrier 14 is normally driven in a forward lateral direction indicated by the arrow F by carrier moving means including a coil spring motor or stored energy bearing means 21 having a spring 22 that is connected to the carrier 14 by suitable cord or cable 23 which is wound about capstan 2.4. A constantly rotating motor 25 connected to a power shaft 26 through a belt transmission 27 supplies power for driving the carrier 14 in a rearward lateral direction, as indicated by the arrow R to provide, for example, a carrier return, and for winding the coil spring 22. A selectively operable spring clutch 28 controlled by mechanism (not shown) selectively connects a spring motor shaft 29 with the power shaft 26 for producing reverse movement of the carrier 14. The control mechanism for clutch 28 can be like that disclosed in US. Patent 2,902,133, entitled Typewriter Carriage Return and Indexing Mechanism, issued to Neil D. Walton and Henry R. Kruspe, Sept. 1, 1959.

Normal letter feeding escapement of the carriage 14, i.e., step-by-step movement of the carriage in the forward lateral direction as indicated by arrow F, is controlled by mechanism substantially like that shown in U.S. Patent 3,126,998 mentioned above. The normal escapement control mechanism of this invention comprises a pair of cscapement control members, viz. a multitoothed escapement gear or rack member 31 that extends substantially the full length of carrier movement, and for purposes of normal escapement, is held stationary with respect to the frame 11, and an escapement pawl member 32 that is supported .by pivot stud 33 on the carrier 14 for movement therewith. Pawl 32 is biased by a spring 34 into normal engagement with the teeth of the rack 31.

The teeth of the rack 31 are constructed to provide one fiat or holding face 31a (see FIGURE 2A) and a permis sive movement, ratcheting or cam face 31b. These faces cooperate with respective forward and rearward pawl surfaces 32a. and 32b. Rack-tooth holding face 31a and pawl surface 32a provide an effective force transmitting abutment to resist any tendency for relative lateral movement between the rack 31 and the pawl 32. Conversely, racktooth camming face 311) and pawl cumming surface 325 cooperate by a camming or ratcheting engagement which is ineffective to prevent relative lateral motion between the rack 31 and the pawl 32.

The pawl 32 is provided with a finger 35 that overlies a trigger bail 41 so as to be actuatable thereby at any location along the length of the platen 12. The trigger bail 41 is pivotally mounted by a stud 42 on the frame 11 and is biased by a spring 43 to a normal permit-pawl-in-rack position. Trigger lever 44 operates under the influence of an escapement cycle cam 45 that is driven by the power shaft 26 upon operation of a selectively operable spring clutch 46 substantially as described in the aforesaid U.S. Patent No. 3,126,998. Trigger lever 44 is selectively driven through follower 44a, connecting link 4412 and rock arm 44c, and pivots bail 41 clockwise for a predetermined time period until a hook finger 44d overruns bail trigger plate 41a. When freed from hook finger 44d, bail 41 is restored to its normal position by spring 43. The tilting of escapement bail 41 pulls the pawl 32 out of the rack 31, allowing the spring 22 to pull the cable 23 and move the carriage 14 in forward lateral direction F. The timed release of the escapement bail 41 causes the pawl 32 to drop into the next rack tooth and abut a surface 31a to halt the forward movement.

Selection of a normal escapement operation is usually performed upon the print of any character and also upon the selection of an interword space as by a space bar 47. For purposes of simplicity, FIGURE 1 shows a key lever 48 having a latching shoulder 48a that is biased .by a spring 49 into clutch arresting or disengaging cooperation with the clutch 46. It will be seen that depression of the space bar 47 will cause the latching shoulder 48a to release the spring clutch 46 providing driving connection between the shaft 26 and the cam 45 to cause an operation of the trigger lever 44. The space bar 47 is released immediately after depression allowing the spring 49 to restore the latch 48a to an upward position where it arrests the spring clutch 46 after 180 of rotation. It is to be understood that more sophisticated key lever mechanisms such as that of U.S. Patent No. 3,126,998 can be interchanged with that shown herein without departing from the scope of this invention.

Step-by-step back spacing, i.e., movement of the carrier 14 in the lateral direction of arrow R (see FIGURE 2A), is obtained .by moving the rack 31 in lateral direction R to transmit force through the pawl 32 to displace the carrier 14, then quickly restoring the rack to its original position. The rack 31 is mounted by screws or studs 36 On the frame 11 which ride in rack slots 37 to permit limited lateral movement thereof. A normally non-operative spring or similar resilient means 38 is connected to the rack 31 to urge when operative, the rack teeth cam faces 31b against and past pawl cam surface 32b. Selectively operable actuating means 50 comprising a spring clutch 51, backspace cycle cam 52 having a high acceleration surface or contour 52a for abrupt rack unloading, a follower 53 biased thereagainst by spring 53a, pull rod 54, floating link 55, and connecting links 56a and 56b, is operative to force the escapement rack 31 back one space from datum D (see FIGURE 213), thus driving the carriagc 14 back one space through interaction of rack-tooth face 31a and pawl tooth surface 320.

The actuating mechanism automatically (due to cam contour 52a) causes an abrupt release or unloading of the rack 31. At this point in time, the carriage 14 is tending to move in the forward lateral direction F under the influence of coil Spring 22 since the rack 31 is no longer held stationary by studs 36. The rack 31 is also tending to accelerate to the left of FIGURE 1 under the influence of its spring 38. The rack 31 has much less mass than the carriage 14 and thus is capable of much more rapid acceleration than carriage 14. Accordingly, the rack 31 escapes to the left past the pawl 32 thus locating the pawl in a succeeding rack-tooth 31 and effectively preventing return movement of the carrier 14 (see FIGURE 2C). The carrier 14 is now positioned one step rearwardly from its starting position.

A backspace key 57 is mounted on a simplified key lever 58 having a latching shoulder 58a that is biased by spring means 59 into engagement with the clutch 51 to control operation of the backspace mechanism in a manner similar to that described in connection with the normal escapement control.

In manual typing it is often necessary to make corrections involving the insertion of additional characters into a limited space. It is not possible to employ the normal escapement mechanism during such crowded typing due to the fixed Spacing relationship dictated by normal escapement. This invention includes rack displacement means 60 comprising a printing station adjustment control lever 61 pivoted at 62 to the frame 11 and connected to an end a of the link 55 by positioning connection 63. Link 55 and link 56a connected thereto are thus manually movable to the left of FIGURE 1 to thereby pivot the link 56b clockwise and displace the rack 31 slightly to the right or in the rearward lateral direction as necessary to provide a modified spacing. In other words, movement of the control lever 61 manually adjusts the datum or home position of the escapement rack 31, to permit a limited variability of the printing station for correction of errors and other operator orientated functions. Friction holding means such as a high friction surface 64 is provided to maintain the displacement during a print cycle, for example.

Those skilled in the art will appreciate that this invention provides a simplified, highly reliable escapement control mechanism for producing both forward and rearward escapement control with a single rack and paw]. Of course, selectable alternative single racks and single pawls could be employed to provide multiple pitch operation, without departing from the single rack concept disclosed herein. It will further be appreciated that much of the same mechanism employed to perform the back spacing operation is employed to provide a manually selectable printing station adjustment to add a new dimension in flexibility for operator convenience. While a specific embodiment of this invention has been shown for purposes of illustration, it is to be understood that various modifications in the specific structure shown, and in the relative operational relationships, i.e., between fixed and movable parts, can be made without departing from the spirit and scope of this invention as particularly pointed out and defined in the appended claims.

We claim:

1. In combination with a printing device having a stationary frame, a platen, and print forming means defining a printing station with respect to the platen, One of the platen and print forming means being mounted on a laterally movable carrier; wherein the improvement comprises means for moving the carrier to displace the printing station lengthwise of the platen including:

a pawl member having a holding surface and an op posed camming surface,

a gear member having a plurality of adjacent teeth each having a holding face and an opposed camming face for cooperating respectively with the holding surface and camming surface of said pawl member,

means resiliently biasing said pawl member into cooperative engagement with teeth of said gear member,

one of said pawl and said gear members having a low mass with respect to the carrier and being movably supported on the frame,

the other of said pawl and said gear members being operatively connected to the carrier such that a correlation is provided between its position and the position of the carrier,

resilient urging means operatively connected to said one member independently of the carrier and oriented for urging said pawl camming surface toward cooperation with a gear-tooth camming face,

selectively operable actuating means drivingly connected to said one member independently of the carrier for moving said one member against said resilient urging means and transmitting force between said pawl holding surface and a gear tooth holding face to displace the carrier laterally in one direction with respect to the frame, said actuating means including means for abruptly unloading said one member to render said resilient urging means operative to cause relative movement of a tooth camming face of said gear member against and past the camming surface of said pawl member.

2. The combination defined in claim 1 wherein said print forming means is mounted on the laterally movable carrier.

3. The combination defined in claim 1 wherein said gear member is supportedly mounted on the frame and said pawl member is operatively connected to the carrier such that a correlation is provided between its position and the position of the carrier.

4. The combination as defined in claim 3 wherein said multitooth gear member is a rectilinear rack extending substantially along the entire range of movement of the laterally movable carrier.

5. The combination as defined in claim 4 comprising further means for displacing said rack relative to said frame and for holding said rack in a displaced position at least during one complete operation of said print forming means.

6. The combination as defined in claim 1 further comprising:

energy bearing means operatively connected to the carrier tending to move the carrier laterally relative to the frame and urging said pawl holding surface and said gear-tooth holding face into force transmitting engagement, and

means overcoming said resilient biasing means for temporarily disconnecting said pawl member from said gear member to permit predetermined lateral movement of the carrier by said energy bearing means.

7. The combination as defined in claim 6 further comprising a constantly rotating power shaft, and wherein said energy bearing means comprises an energy storing spring operatively connected to the carrier, and a first selectively operable clutch for supplying energy from said constantly rotating shaft to said energy storing spring,

said pawl member disconnecting means comprises a trigger, a first cam operatively connected to said trigger for driving said trigger through an operating cycle, and a second selectively operable clutch for connecting said first cam to said constantly rotating shaft,

and said selectively operable actuating means comprises a second cam, a follower for said second cam, means connecting said follower to said one of said pawl and said gear members, said second cam having a contour causing abrupt unloading of said one of said pawl and said gear members, and a third selectively operable clutch for connecting said second cam to said constantly rotating shaft.

References Cited UNITED STATES PATENTS 580,014 4/1897 Souder 19784 X 633,139 9/1899 Killman et a1 19785 X 913,306 2/1909 Richards 197-86 X 1,254,501 1/1918 Henry. 1,639,199 8/1927 Peeters 197-91 1,798,610 3/1931 Lasker 197-91 X 2,577,467 12/1951 Kloski et al. 19791 2,741,355 4/1956 Dodge 19786 2,818,958 1/1958 Toeppen et al. 19785 2,902,133 9/1959 Waiton et a1. 19766 2,919,002 12/1959 Palmer 19716 3,126,998 3/1964 Palmer 19782 3,263,793 8/1966 Brignole 197-66 X 2,522,896 9/ 1950 Rifkin et al.

FOREIGN PATENTS 29,363 1909 Great Britain.

ROBERT E. PULFREY, Primary Examiner. E. T. WRIGHT, Examiner. 

